Bridge



(No Model.)

A. S. DANDRIDG-E.

BRIDGE.

. Patented Dec. 21,1897.

WITNESSES NITED STATES ATENT BRIDGE.

. f r v SPECIFICATION forming part of Letters Patent No. 595,906, dated December 21, 1897.

Application filed March 31 1397- To all whom it may concern:

Be it known that I, ALEXANDER SPOTS- woon DANDRIDGE, a citizen of the United States, and a resident of Brooklyn, in the county of Kings, State of New York, have invented certain new and useful Improvements in Bridges, of which the following is a specification sufficient to enable others skilled in the art to which the invention appertains to make and use the same.

My invention relates to improvements in bridges of that class termed suspensionbridges, in which the roadway is supported on trusswork suspended by ties from main suspension-cables which are carried over towers at either end and suitably anchored.

The main objects of my invention are to strengthen the bridge structure, increase the rigidity and obviate objectionable and dangerous vibration, to impart great stiifness and resistance to pressure, and to thoroughly distribute the loads.

To this end my invention consists of a suspension-bridge which has above the main cables a separate or auxiliary truss structure of suitable rigidity and strongly braced, the lower chord of which truss conforms in curvature to the curve of the main cables and which is placed upon said main cables and suitably secured thereto. The invention consists, further, of details of construction hereinafter described, and defined in the claims.

Referring to the drawings, Figure 1 is a view in elevation of an ordinary suspensionbridge with my auxiliary truss in position thereon. Fig. 2 is a vertical transverse crosssection, enlarged. Fig. 3 is an elevation of a portion of the bridge and auxiliary truss, also enlarged.

Similar letters of reference sponding parts.

In the drawings, A represents the roadway of a suspension-bridge of any ordinary or approved form, which is supported by vertical ties 66 from a series of main suspension-cables B in the usual manner. The main cables B indicate correare led over suitable towers and are anchored at each end in the manner usual to such structures. In the drawings five pairs of these main cables 13 are shown; but the number may be varied according to circumstances and depends upon the size of the bridge and Serial No. 625,879. (No model.)

the weight intended to be imposed thereon. The roadway may be adapted for any kind of travel, though, as shown, railroad purposes only are contemplated. The auxiliary truss structure 0 is constructed of suitable framework, of metal or wood, strongly braced by cross-beams, so as to provide a truss structure of maximum strength and rigidity. This truss C may be constructed of one rigid framework or it may be made in sections and suitably riveted together. The truss C may be made long enough to extend from one tower to the other or it may be constructed so as to extend only a portion of the distance between said towers.

The truss is preferably made in the form of a crescentthat is to say, its greatest height is at the center, from which point it gradually tapers in a curve toward each end. The lower chord of the truss has substantially the same curvature as that of the main cables, upon which it rests, while the upper chord has a curvature considerably less than the lower, or the upper chord may be substantially a straight line or may even be convexed, so as to give the truss the shape of a lens or double convex. The degree of structural strength and rigidity required will determine the shape of the truss, but for ordinary purposes the form illustrated will be found adequate. Girders or beams O are firmly attached to the upper surfaces of the main cables, upon which the auxiliary truss O rests and to which it is firmly and rigidly secured. The vertical ties at, by which the roadway-truss is supported, are shown as secured to the framework of the auxiliary truss. This construction gives greater rigidity and strength, and hence is preferred; but it is obvious that these ties a may be secured to the main cables above or to both the main cables and the auxiliary truss or in any other suitable manner, as to the cross beams or girders 0''. So, also, the auxiliary truss structure may have all web members and chords both ties and struts, or the web members maybe all struts acting as ties and struts, or both chords may be struts. The auxiliary truss may also be constructed of plate-girders,

with solid or open web, the object sought being 7 to provide an auxiliary truss so constructed as to possess the maximum strength and rigidity consistent with lightness and bulk.

The auxiliary truss O is preferably secured to the main cables or to the crossgirders which are secured to the main cables at or about the center of span only, allowing all other portions of the auxiliary truss to move freely on its supports; or the truss C may rest upon the cross-girders 0 without any rigid fastening to the main cables or to its supports, suitable guides or ways being provided upon said cross-girders C to prevent lateral displacement, but permitting free movement in said guides or ways. It is obvious also that the auxiliary truss may be' rigidly secured throughout its entire length to the cables or cross-girders or only at the ends thereof; also, that independent cables may be provided to which said auxiliary truss may be secured. The lower or roadway truss may be either en tirely below the main cables or partly below and partly above said cables, in which latter case the framework of the auxiliary truss and that of the roadway must be suitably spaced, so that they will not interfere. The cross girders or beams C, upon which the auxiliary truss rests, in connection with the truss itself, not only give great rigidity to the bridge against lateral or wind pressure, but these cross-beams take the horizontal strains that would otherwise be thrown on main cables when the main cables are cradled, as is usual in such structures.

Having thus described my invention, I claim as new and desire to secure by Letters Patent- 1. In asuspension-bridge, the combination, with the main suspension-cables, a roadway and the usual truss structure, of an auxiliary truss independent of said truss structure superimposed upon said main cables, substantially as set forth.

2. In a suspension-bridge, the combination,

with the main suspension-cables, and the usual truss structure, of an auxiliary truss separate from and independent of said truss structure, secured upon said cables and a roadway suspended. therefrom, substantially as set forth. 3. In a suspension-bridge, the combination of the main suspension-cables, a roadway, cross-girders secured to said cables and an auxiliary truss suitably secured thereon, substantially as set forth.

4. In a suspension-bridge, the combination of the main cables, crossgirders secured i thereto, an auxiliary truss secured at its central portion to said cross-girders, and a roadway suspended from the auxiliary truss, substantially as set forth.

5. In a suspension-bridge, the combination of the main cables, a roadway, the usual truss structure and an auxiliary truss independent of said truss structure, superimposed upon said main cables and constructed of a rigid framework having an upper and a lower chord, the curvature of the lower chord conforming with the curvature of the main cables, substantially as set forth.

ALEXANDER SPOTSWOOD DANDRIDGE.

\Vitnesses:

CHARLES WILLIAM GRESLEY LEE, EDWARD PARRISH. 

